I've been thinking about why we think about thinking

Several philosophers claim to have had the following conversation on long-haul flights: "And what line of work are you in?" "Me? I'm a philosopher." "Oh, really? And what are some of your sayings?"

It is, of course, intended to illustrate the deplorable ignorance of the sort of person - probably, heaven help us, an American woman - who might attempt to be pleasant to an odd-looking stranger. How dare she! And to compound such a sin with the misapprehension that philosophy has something to do with wisdom ...

Philosophers are rarely at ease when invited to ruminate in public, especially if they don't have their notes handy. In Pinter's The Homecoming, Teddy, a professor of philosophy who has been teaching in the US, pays a surprise visit to his unsettling brothers still living in the family home in London. Streetwise brother Lenny gamely tries to engage Teddy in philosophical discussion, asking: "Do you detect a certain logical incoherence in the central affirmations of Christian theism?" Teddy replies: "That question doesn't fall within my province." A little later, Lenny tries again: "What do you make of all this business of being and non-being?" Teddy, it seems, makes nothing of it.

Brilliantly observed. Pinter must already have been a veteran of Hampstead and Oxford dinner parties, where such awkward conversational moments are served up alongside the limp asparagus. I saw The Homecoming as an undergraduate, and resolved that if I were ever lucky enough to be paid out of the public purse to think about philosophy, every taxpayer would have the right to seek my opinion on any philosophical question. They'd be lining up, I was sure.

As time goes on, that sense of my responsibilities has faded, and I get a sinking feeling when someone asks me what I do. I tend to reply that I teach political philosophy, and prepare myself for a tirade against Blair. Mentioning "moral philosophy" would lead to unimaginable horrors. I can't even bring myself to read the journal Ethics on the tube in case someone thinks I am a vicar.

How should we answer when asked what we do? One friend says she is an "ontologist". As no one can quite be sure whether this is branch of philosophy or a cancer specialism, the conversation moves soothingly on to house prices.

Why are we so worried about revealing ourselves? After all, most of us are proud of what we do. It just sounds horribly pretentious. It is one thing to teach philosophy, even to write philosophical articles, another to be a philosopher, which has connotations of depth, charisma and calm, not forgetting originality and insight. There is something of what we philosophers like to call a "pragmatic contradiction" in claiming this for oneself. Posterity, not my contract of employment, will decide whether or not I am a philosopher.

Perhaps the root of our problem is a deep-seated anxiety about what we do and why we do it. From time to time, questions bubble up about the value of education and the use of public funding. The importance of medicine, science and technology are taken for granted, but the arts and humanities are constantly in a state of having to justify themselves. If we take the question on its own terms, and point out how business-friendly our subjects are, we are accused of having an "instrumental" approach to education. If, on the other hand, we make a passionate defence of the intrinsic value of our subjects, we are accused of snobbery and elitism.

There is only one solution to this: a proper public relations campaign. How about this for a slogan (or should that be a saying?): "Medicine helps us live longer; scientific advance saves us time; but the arts and humanities make it worth living longer, with time on our hands." All right, all right, I know it isn't very snappy. What do you expect? I'm a philosopher, not an advertising copywriter. And no, actually, I can't tell you the meaning of life, but what do you think about that Ken Livingstone and congestion charging?

· Professor Jonathan Wolff is head of philosophy at University College London. His column appears monthly